Ras plays an essential role in oncogenic transformation and genesis. Oncogenic H-, K-, and N-Ras arise from point mutations limited to a small number of sites (amino acids 12, 13, 59 and 61). Unlike normal Ras, oncogenic ras proteins lack intrinsic GTPase activity and hence remain constitutively activated (Trahey, M., and McCormick, F. (1987) Science 238: 542-5; Tabin, C. J. et al. (1982) Nature. 300: 143-9; Taparowsky, E. et al. (1982) Nature. 300: 762-5). The participation of oncogenic ras in human cancers is estimated to be 30% (Almoguera, C. et al (1988) Cell. 53:549-54).
Mutations are frequently limited to only one of the ras genes, and the frequency is tissue- and tumor type-specific. K-ras is the most commonly mutated oncogene in human cancers, especially the codon-12 mutation. While oncogenic activation of H-, K-, and N-Ras arising from single nucleotide substitutions has been observed in 30% of human cancers (Bos, J. L. (1989) Cancer Res 49, 4682-9), over 90% of human pancreatic cancer manifest the codon 12 K-ras mutation (Almoguera, C. et al. (1988) Cell 53, 549-54; Smit, V. T. et al. (1988) Nucleic Acids Res 16, 7773-82; Bos, J. L. (1989) Cancer Res 49, 4682-9). Pancreatic ductal adenocarcinoma, the most common cancer of the pancreas, is notorious for its rapid onset and resistance to treatment. The high frequency of K-ras mutations in human pancreatic tumors suggests that constitutive Ras activation plays a critical role during pancreatic oncogenesis. Adenocarcinoma of the exocrine pancreas represents the fourth-leading cause of cancer-related mortality in Western countries. Treatment has had limited success and the five-year survival remains less than 5% with a mean survival of 4 months for patients with surgically unresectable tumors (Jemal, A et al (2002) CA Cancer J Clin 52, 23-47; Burris, H. A., 3rd et al. (1997) J Clin Oncol 15, 2403-13). This point mutation can be identified early in the course of the disease when normal cuboidal pancreatic ductal epithelium progresses to a flat hyperplastic lesion, and is considered causative in the pathogenesis of pancreatic cancer (Hruban, R. H. et al (2000) Clin Cancer Res 6, 2969-72; Tada, M. et al. (1996) Gastroenterology 110, 227-31). The regulation of oncogenic K-ras signaling in human pancreatic cancer, however, remains largely unknown.
K-ras mutations are present in 50% of the cancers of colon and lung (Bos, J. L. et al. (1987) Nature. 327: 293-7; Rodenhuis, S. et al. (1988) Cancer Res. 48: 5738-41). In cancers of the urinary tract and bladder, mutations are primarily in the H-ras gene (Fujita, J. et al. (1984) Nature. 309: 464-6; Visvanathan, K. V. et al. (1988) Oncogene Res. 3: 77-86). N-ras gene mutations are present in 30% of leukemia and liver cancer. Approximately 25% of skin lesions in humans involve mutations of the Ha-Ras (25% for squamous cell carcinoma and 28% for melanomas) (Bos, J. L. (1989) Cancer Res. 49:4683-9; Migley, R. S. and Kerr, D. J. (2002) Crit Rev Oncol Hematol. 44:109-20).50-60% of thyroid carcinomas are unique in having mutations in all three genes (Adjei, A. A. (2001) J Natl Cancer Inst. 93: 1062-74).
Constitutive activation of Ras can be achieved through oncogenic mutations or via hyperactivated growth factor receptors such as the EGFRs. Elevated expression and/or amplification of the members of the EGFR family, especially the EGFR and HER2, have been implicated in various forms of human malignancies (as reviewed in Prenzel, N. et al. (2001) Endocr Relat Cancer. 8: 11-31). In some of these cancers (including pancreas, colon, bladder, lung), EGFR/HER2 overexpression is compounded by the presence of oncogenic Ras mutations. Abnormal activation of these receptors in tumors can be attributed to overexpression, gene amplification, constitutive activation mutations or autocrine growth factor loops (Voldborg, B. R. et al. (1997) Ann Oncol. 8:1197-206). For growth factor receptors, especially the EGFRs, amplification or/and overexpression of these receptors frequently occur in the cancers of the breast, ovary, stomach, esophagus, pancreatic, lung, colon neuroblastoma.
While various therapeutic strategies have been developed to inactivate key components of the Ras-Raf-MAPK cascade, specific inhibition of gain-of-function or constitutive Ras (gƒRas) action has not been achieved clinically (Adjei, A. A. (2001) J Natl Cancer Inst 93, 1062-74; Cox, A. D. & Der, C. J. (2002) Curr Opin Pharmacol 2, 388-93).
Therefore, in view of the aforementioned deficiencies attendant with prior art methods to inactivate or inhibit the Ras pathway, and particularly Ras-mediated cancers, it should be apparent that there still exists a need in the art for methods and compositions for specific inhibition of the Ras pathway and particularly for inhibition of gƒRas.
The citation of references herein shall not be construed as an admission that such is prior art to the present invention.